The present invention relates to a method for transmitting data from a source network device to a destination network device. The present invention also relates to an address conversion apparatus for implementing the method. In this context, network devices can be understood to be network nodes in a communication and/or data network, router devices, network modules, networked personal computers and other communication and data processing devices which can be coupled to a network.
In order to switch data quickly within a network, the data are frequently transmitted in the form of data packets provided with a hardware address as destination address. Hardware addresses, which are also referred to as MAC addresses (medium access control), are addresses which are used in the data link layer (layer 2) of the OSI reference model and with which network devices (usually network modules) are provided by the manufacturer. The hardware address for a network device is stored permanently, i.e., unalterably, in the network device and is unique throughout the world.
Switching data packets on the basis of hardware addresses is typical, particularly in local area networks (“LANs”). A data packet which is provided with a hardware address for a destination network device and is sent to a LAN is recognized by the destination network device in question as being addressed to it from the hardware address and is, therefore, received for further processing or forwarding. Normally, hardware addresses are used only for addressing network devices within a local area network. If a transmission destination is situated outside the local area network, the data packets are generally transported to a router device for the local area network, which router device transfers the data packets using a network address which is additionally contained in the data packets and identifies the transmission destination. Unlike a hardware address, a network address is resident above the data link layer and can be reversibly assigned to a network device via system administration. The network addresses used are frequently “Internet Protocol addresses”, also referred to as “IP” addresses below. The router device evaluates the network address in the data packets and, on the basis of this, determines an address information item identifying a destination network device which is registered in the router device and is as close as possible to the transmission destination or is possibly identical thereto. The data packets are then transferred to this destination network device using the address information item. If this destination network device does not match the ultimate transmission destination, this destination network device is responsible for transferring the data packets toward the transmission destination.
A method allowing data packets provided with an IP address to be transferred transparently via an ATM network (ATM: asynchronous transfer mode) to a transmission destination which is coupled to the ATM network and is identified by the IP address is known by the name IpoA (IP over ATM), for example. In this context, a router device uses the IP address in the data packets to determine the ATM address of an ATM exit network node which is as close as possible to the transmission destination and is used to forward the data packets in the ATM network. Aspects of this method are described in Internet specification RFC 2225, for example.
However, the evaluation of IP addresses for alternate routing which these methods require is a relatively complex operation which can generally be implemented only with a high level of circuit complexity.
It is an object of the present invention, therefore, to specify a method for transmitting data from a source network device to at least one destination network device which requires less complex address evaluation. It is also an aim to specify an address conversion apparatus for implementing the method.